1. Field of the Invention
This invention relates to a power MOSFET made up of a plurality of individual MOSFET's connected in parallel, and more particularly to a power MOSFET of this type including a sensing MOSFET coupled in parallel with the power MOSFET, wherein a resistor is coupled between the source of the sensing MOSFET and the source of the power MOSFET.
2. Background of the Invention
A MOSFET related to this type has been described in the Feb. 20, 1986 issue of Electronic Design at pages 59-60. The power MOSFET (transistor) consists of thousands of individual, tiny MOSFETs, all connected in parallel and all passing virtually equal currents through equal on-resistances. One or more of the individual MOSFETs are used as sense transistors which have their sources disconnected from those of the other MOSFETs and connected to a sense pin on the MOSFET package. Another pin (Kelvin pin) on the package is linked to the power MOSFET's source and a current sensing resistor is connected between the sense pin and Kelvin pin. The voltage across the resistor is a direct linear function of the current passing through the power transistor. This voltage thus can be used to monitor the current passing through the power transistor. Since only a very small fraction of the power transistor current is used for such monitoring, the power loss produced in the resistor is relatively small.
The above-described power MOSFET requires a different design from that of a regular power MOSFET that otherwise has the same electrical properties, and this different design requires additional cost.